The disclosure of Japanese Patent Application No. H11-288979 filed Oct. 12, 1999 is herein incorporated by reference.
1. Technical Field
The present invention relates to a laser microscope and a confocal laser scanning microscope.
2. Background Art
The limits to the resolving power of a microscope employed to observe an ultra-fine structure is normally a expressed as xcex4=xcex/2NA with xcex4 representing the resolving power, xcex representing the operating wavelength and NA representing the numerical aperture at the objective lens. This expression indicates that the resolving power xcex4 maybe improved by reducing the operating wavelength xcex, by increasing the numerical aperture NA at the objective lens or by both reducing the operating wavelength xcex and increasing the numerical aperture NA of the objective lens at the same time.
When observing a bio-sample (bio-specimen) such as a cell, the resolving power is improved by utilizing an immersion objective lens, since if the operating wavelength was reduced to a value at or lower than the ultraviolet range (equal to or lower than 300 nm), the sample itself would become damaged due to a photochemical reaction or the like occurring in the sample.
If, the other hand, the sample is mainly constituted of an inorganic material and, in particular, when observing an integrated circuit, the sample is not subject to extensive damage and, thus, the resolving power is improved by reducing the operating wavelength unlike when observing a bio-sample.
Under normal circumstances, the use of immersion objective lenses is not desirable since oil would adhere to the sample to result in oxidation of metal wirings thereby inducing problems such as shorting of the integrated circuit.
However, the reduction in the operating wavelength would complicate the structure and the operation of a microscope system that operates in the wavelength range of X rays or electron beams, which is bound to compromise the ease of use and, therefore, there is a limit to the degree to which the operating wavelength can be reduced.
Miniaturization of all ultra-fine structures, a typical example of which is an integrated circuit such as an IC, has been vigorously pursued in recent years in the field of semiconductors. In the case of an ultra-fine cyclical structure (xe2x80x9cline and spacexe2x80x9d is terminology normally used in the semiconductor process technology), it becomes logically difficult to resolve a cyclical structure in the sample with its repetitive cycle smaller than 0.25 xcexcm with good contrast on a conventional optical microscope.
However, a resolving power of 0.10 xcexcm is achieved by using a deep ultraviolet continuous oscillation laser as a light source and using an objective lens with a large numerical aperture of approximately 0.9. Deep ultraviolet continuous oscillation lasers include a laser that continuously oscillates light with a wavelength of 266 nm which is a quadruple harmonic of Nd:YAG laser by using a BBO crystal
While an inorganic sample is not subject to extensive damage to the sample caused by deep ultraviolet light compared to a bio-sample, some damage still does occur to such an inorganic sample. For instance, if the sample is a resist pattern on a semiconductor wafer, the wavelength of light used to expose the resist during the manufacturing process is close to the wavelength of light irradiated on the sample during an observation and the total exposure quantity is large, the sample becomes damaged.
In particular, the use of a confocal laser scanning microscope poses a problem in that since the laser light converges within a very small range at the surface of the sample to result in a high level of energy received at the sample per unit area, the degree of damage increases compared to that associated with one shot illumination (Kohler illumination).
An object of the present invention is to provide a laser microscope and a confocal laser scanning microscope that minimize damage to a sample caused by deep ultraviolet light.
In order to attain the above object, a laser microscope according to the present invention comprises: a light source that emits deep ultraviolet laser light to be irradiated on a sample; a limiting device that sets a limit to an intensity of the deep ultraviolet laser light irradiated on the sample; a detection device that detects the deep ultraviolet laser light having been reflected from the sample; a storage device that stores first information related to damage to the sample corresponding to the intensity of the deep ultraviolet laser light; and a control device that controls the limiting device based upon the first information when a sample damage limit is input from outside.
A confocal laser scanning microscope according to the present invention comprises: a light source that emits deep ultraviolet laser light to be irradiated on a sample; a limiting device that sets a limit to an intensity of the deep ultraviolet laser light irradiated on the sample; a detection device that detects the deep ultraviolet laser light having been reflected from the sample; a pinhole device provided frontward relative to the detection device and having a pinhole for limiting the reflected light; a storage device that stores first information related to damage to the sample corresponding to the intensity of the deep ultraviolet laser light; and a control device that controls the limiting device based upon the first information when sample damage limit is input from outside.
In this confocal laser scanning microscope, it is preferred that the pinhole device controls a pinhole size when a pinhole adjustment signal is input from outside.